Part One: Aerosol Transmission of Disease
In a July 6th “invited commentary” in Clinical InfectiousDiseases,239 scientists urged the CDC and WHO to acknowledge that COVID-19, the infection transmitted by the SARS-CoV-2 virus, was spread via airborne droplets. To that point, the WHO (and the CDC) had dismissed the possibility that COVID could be an airborne-transmitted infection.
In the commentary, clinicians and scholars pressed the WHO to recognize the airborne transmission route of SARS-CoV-2. They provided – and demanded attention to - the growing body of evidence which established “beyond any reasonable doubt” that the virus spreads indoors through tiny aerosols — and that the WHO’s recommendations should fundamentally change.
But the WHO wasn’t easily persuaded. In response to the July 6th commentary, Benedetta Allegranzi, the WHO’s technical lead on infection control, responded to the New York Times, with stubborn doubts about COVID and airborne transmission, “Especially in the last couple of months, we have been stating several times that we consider airborne transmission as possible but certainly not supported by solid or even clear evidence.”
To that point, six months into the unfolding pandemic, clinicians, and caregivers were advised that hand-washing and hygiene may be adequate prevention measures. The WHO and CDC positions were that viral droplets were so large that they could only land on near surfaces, and therefore not capable of longer distance contagion via aerosolization.
And now, we look back to the days of Eisenhower in 1954.
Surely, the WHO and CDC had known of William F. Wells, the “eccentric genius and originator of the droplet nucleus hypothesis... demonstrator of droplet nucleus transmission of bovine TB in rabbits.”
The WHO and CDC had to have known that in 1954, Wells andRiley, droplet nuclei experts working at a VA hospital, proved those droplet nuclei could travel through the air, through ventilation systems, and infect others from the infectious source, many rooms away.
Their paper was published in 1962, 58 years before the COVID outbreak and the contentious discussions over the ability of droplet nuclei to travel through the air. Wells and Riley had already proven it, however, whenEisenhower was in the White House.
Wells and Riley also developed an equation which could help to mathematically formulate a risk assessment model for infection. The model considers many of the complex variables that influence disease transmission and infection potential.
From “Review and comparison between the Wells–Riley and dose‐response approaches to risk assessment of infectious respiratory diseases,” a number of influencing factors affect this infection process and the outcome.They are listed in Table 1. These factors add complexities to the exposure and risk assessment of pathogenic microorganisms. Many of them are not well‐understood, especially the pathogen–host interactions. As a result, statistics and probabilities are often employed to formulate quantitative infection risk, assessment models.
TABLE  – from “Review and comparison between theWells–Riley and dose‐response approaches to risk assessment of infectious respiratory diseases”
Those who cared for the first wave of COVID patients, including physicians and nurses, were told that the COVID-19 disease was transmitted through surfaces and direct patient contact, and that there was little evidence to support transmission via an airborne vector.
When the CDC and WHO finally acknowledged the spread ofCOVID via aerosolized droplets, the pandemic was well underway.
As Wells and Riley had proven in 1954, the public and caregivers were finally told the air wasn’t safe.
Not only could coughing and sneezing transmit the disease, but it was found that even the breath of an infected person was infectious. Other aerosol reservoirs were discovered as well, including centralized, public, single, and shared plumbing systems. The aerosolization of biofilms and surface droplets. Centralized HVAC and ventilation systems.
Once the airborne vector was acknowledged, isolation, masking, contact tracing, and other PPE helped to slow the spread of the pandemic, giving the world time to develop and distribute the now historic mRNA vaccines.
The president of the World Health Organization acknowledged in a May 2021 address that over 115,000 healthcare workers have died from COVID-19 infections worldwide.
“Speaking at the opening of theWHO's main annual assembly, Tedros Adhanom Ghebreyesus paid tribute to the work of health care professionals worldwide, noting that "many have themselves become infected, and while reporting is scant, we estimate that at least115,000 health and care workers have paid the ultimate price in the service of others."
We’ve moved into an era of astounding public transformation.We’ve all become more knowledgeable about clean, safe air. We’re now thinking about whether we’re safe from infection in the workplace, the doctor’s office, the grocery store, and even at home. Many of us no longer accept infection as inevitable. We want to be safe with coworkers, students, and within our communities.
We’ve all become more conscious of our personal space, of our surroundings, and of the potential risk in simply breathing.
Even with a vaccinated public, we’ll continue to be aware of environmental risks to our personal safety and not just about COVID.
Our journey into clean air is just beginning. In part two, we’ll discuss the role of centralized air handling systems (HVAC) in infection prevention.
Lidia Morawska, Donald K Milton, It Is Time toAddress Airborne Transmission of Coronavirus Disease 2019 (COVID-19), Clinical Infectious Diseases, Volume 71, Issue 9, 1 November 2020, Pages 2311–2313, https://doi.org/10.1093/cid/ciaa939
 Sze To GN, Chao CY. Review and comparison between the Wells-Riley and dose-response approaches to risk assessment of infectious respiratory diseases. Indoor Air. 2010;20(1):2-16.doi:10.1111/j.1600-0668.2009.00621.x